Go to PepBoys, Advanced Auto, Auto Zone, etc. and have them pull the code. It will most likely be some generic P0XXX, write it down (to Google it later), then have them reset it. If your car is not running funky it's probably something you can ignore. I popped a cat efficiency code once or twice, most likely due to bad gas. Didn't come on until I was just cruising along after going through about half the tank.
2007 WRX TR | Stage 2 | PAR Gearset (Built by AndrewTech)